The present invention relates to radio frequency (RF) communication over a short distance, and more particularly, to the transmission of short range RF communication signals in the presence of constant and intermittent interferers having strong power relative to the communication signal power.
As modern commercial aircraft engines have become increasingly complex, it has become practice to develop and deploy automatic control of various functions in order to prevent stressing of the aircraft crew. One of the signal developments in this discipline has been the Full Authority Digital Engine Control (FADEC). Previously, commercial FADEC technology became operational on large passenger jet aircraft. The FADEC is an aircraft control that performs comprehensive monitoring of vital engine parameters and concomitant adjustment of engine control variables. The control loop realized with the FADEC results in significantly reduced fuel consumption and thereby increased engine efficiency and lower aircraft operating costs. It also promotes greater overall engine reliability.
As aircraft engines have become larger and more complex, it has become desirable to decentralize the FADEC functions. One approach to decentralizing the FADEC functions is to realize the FADEC as a distributed control system composed of two component classes. The first component class constitutes the Remote Digital Electronic Controllers (RDEC). The RDEC are under supervision by the second component class that constitutes the Central Digital Electronic Controller (CDEC). Typically, the controllers, RDEC and/or CDEC, include various sensors.
In a distributed realization of the FADEC, reliable communication between the CDEC and the RDEC is needed. Typically, communication between the CDEC and RDEC uses hardwired cables. This approach is costly and adds significant maintenance overhead if applied to a decentralized FADEC configuration. One approach that has been suggested is to use an extant short range RF communication system. Many RF communication techniques can be used, such as, for example, Bluetooth. Typically, Bluetooth comprises a system approach that was developed with the aim of eliminating cabling between certain electronic modules. Further, Bluetooth is an evolving standard and specification that is supported by a consortium of electronics manufacturers that seek to promote short range wireless communication between mobile electronic devices. Another communication technique is the IEEE standard 802.11. Typically, the IEEE standard 802.11 is used for wireless local area networking and specifies a communications protocol known as carrier sense multiple access/collision avoidance (CSMA/CA). Both the Bluetooth and the IEEE standard 802.11 techniques are designed to operate in fixed and controlled frequency bands that can have the frequencies of operation vary according to geographic region.
However, extant short range RF communications techniques, such as, Bluetooth, IEEE standard 802.11, and other standard or proto-standard techniques are not entirely suitable for use in a decentralized FADEC because of significant electromagnetic interference (EMI) that exists in the operating environment of the CDEC and RDEC. The EMI that exists in the operating environment is caused by various sources, such as, for example, radar and strong communication signals. The strong communication signals interference can be considered as approximately continuous in time and of long persistence. However, the radar interference is different in its interference characteristics. Typically, radar interference characteristics have two types. The first type is so-called square wave pulsed radar that typically exhibits a pulse repetition frequency (PRF) of about 300 to about 1000 pulses per second (PPS) with pulse widths of from about 1 to about 3 microseconds. The second type is so-called pulsed radar that typically exhibits a PRF of about 1000 to about 3000 PPS with pulse widths of about 0.25 to about 1.5 microseconds. In addition, the EMI interference can exist on many different frequencies.
The EMI in the communications environment can cause problems with the communication system because of the persistence and duration of the EMI. In addition, the received interference signal power and interference signal spectral content also can cause problems with the communication system. Further, the uncertainty of the EMI interference is also a factor that can cause problems with the communication system. Specifically, strong communication signals may exhibit extended persistence but have a spectral composition of limited width when compared to a radar interfering signal composed of periodic pulses of relatively low duty cycle. However, the limited duration of the radar interference pulses imparts a wide spectral content to the interfering radar signal, and the shorter the pulse duration of the pulse then the wider the interfering spectrum.
Yet another consideration to be considered when adopting a short range RF communications system is the impact the communication system, itself, has on other users. In a first consideration, the Federal Communications Commission (FCC) has promulgated regulations respecting the transmission of radio signals and these regulations must be observed. In a second consideration, the short range RF communications can constitute EMI to control and other electronics within the host aircraft. As a consequence of these considerations, it would be necessary to carefully design RF signaling used for short range communications supporting the FADEC functions.
Finally, another consideration relates to the timeliness of data transport. A common approach to reliable communication over an intermittently highly disturbed RF link is to use a data transport protocol that relies on acknowledgment/non-acknowledgment. Such a technique is typically not used because some of the data to be communicated within the decentralized FADEC does not tolerate the increased latency that may occur using this conventional technique.
Therefore a desire exists to provide operationally reliable RF communications link between a CDEC and RDEC of a decentralized FADEC that is compliant with regulations and compatible with ancillary electronics.